The following patents typify hand exercising devices of various configurations and all including a compressible material:
______________________________________ 2,271,164 Sullivan 3,326,550 Melchiona 3,129,939 Stock 3,413,243 Griffin 3,265,389 Carlson 3,611,807 Brandell ______________________________________
In common, none of the prior art references discloses means for varying the resistance of the exercise device to compression other than the natural resistance of the compressible material itself. By way of example, the Carlson U.S. Pat. No. 3,265,389 includes recesses and holes formed in the elastomeric material to reduce the natural resistance of the material to compression. However, once the recesses or holes are formed in the exercise device, the basic resistance of the device to compression is set and no further variation therein occurs other than due to the material itself.